In general, a quantitative analysis of a target component in a sample using a liquid chromatograph mass spectrometer (LC-MS) is performed as follows: A selective ion monitoring (SIM) measurement or multiple reaction monitoring (MRM) measurement for a mass-to-charge ratio corresponding to an ion originating from the target component is performed within the vicinity of the retention time at which the target component is eluted. Based on the data obtained by the measurement, an extracted ion chromatogram is created. In this extracted ion chromatogram, the area value of the peak corresponding to the target component is calculated. Eventually, the amount or concentration of the target component is calculated from the peak area value using a calibration curve previously created.
In an atmospheric pressure ionization mass spectrometer which is used in a liquid chromatograph mass spectrometer, the generation efficiency and passage efficiency of ions change depending on various control parameters, such as the voltage applied to an ion transport optical system (which is called the “ion lens”, “ion guide” or otherwise), the temperature of the ionization probe in the atmospheric pressure ion source and that of the heated capillary for transporting ions. The optimum values of those control parameters with which the highest levels of ion generation efficiency and ion passage efficiency can be achieved also depend on the mass-to-charge ratio of the ion originating from the target component to be analyzed. Therefore, in order to enhance the accuracy of the quantitative determination for the target component or to improve the lower limit of the quantitative determination (i.e. to decrease the lower limit), it is necessary to set the various aforementioned control parameters at their respective optimum values according to the target component to be analyzed when the measurement is performed. Accordingly, conventional mass spectrometers are provided with the automatic tuning function for automatically searching for the optimum values of the control parameters for each target component beforehand (i.e. in advance of the measurement of the target sample).
As described in Patent Literatures 1, 2 or other documents, the automatic tuning is normally achieved by actually performing a measurement of a target component in a sample while changing the value of the control parameter and by automatically processing the thereby obtained measurement result. When a sample which only contains the target component is used as the sample, an infusion method or flow injection method is normally used to introduce the sample into the mass spectrometer. When a sample which contains a plurality of components in addition to the target component is used, a sample that contains the components which have been separated by a column is introduced into the mass spectrometer.
The primary reason for performing the automatic tuning is to detect a trace amount of component with a high level of sensitivity. Accordingly, in normal situations, the parameter values for controlling each section of the system are adjusted so as to maximize the signal strength of the ion originating from the target component. However, conducting a measurement under the control parameters adjusted in this manner does not always ensure that the highest level of quantitative accuracy and sensitivity is achieved. The reason is as follows: If the background noise within the time range where the target component is eluted is increased due to a foreign substance or other factors, the SN ratio may become lower than the highest possible level even when the signal strength of the ion originating from the target component is maximized. In such a case, the accuracy of the peak area value in the extracted ion chromatogram will be low.